Just wonderful little details like calling Mei Ling while in the woman's bathroom means she calls you a pervert or murdering a bunch of ravens on the elevator down to see Vulcan Raven earns you a telling off from the Codec team and the man himself will be really angry with you shows the love and care that the game was made with.

EDIT: http://metalgear.wikia.com/wiki/Meta..._Solid_secrets

Just trout like this

If Snake is discovered by sentries in the first area of the game, another cutscene will be activated if Snake goes through the second floor ventilation shaft where two guards talk about "another" intruder.

blows my mind.